The present invention relates to a radiation tomographic imaging apparatus and an imaging method, and more particularly to a radiation tomographic imaging apparatus and an imaging method for producing a tomographic image at a predefined position in a subject during a scan.
As an apparatus for capturing a tomographic image, there is known, for example, an X-ray CT (computed tomography) apparatus for emitting X-rays as radiation, detecting X-rays passing through a subject, and arithmetically producing a tomographic image.
The X-ray CT apparatus has a scan gantry comprised of an X-ray tube and a detector array disposed to face the X-ray tube with the subject placed therebetween, and detects X-rays emitted toward the subject from the X-ray tube by the detector array. The X-ray CT apparatus scans the subject placed on an imaging table while, for example, rotating the scan gantry around the subject. Consequently, projection data of the subject are obtained in a plurality of views. The X-ray CT apparatus reconstructs the resulting projection data to produce a tomographic image of the subject of a predetermined slice thickness.
In such an X-ray CT apparatus, there is known a method of producing an image by sequentially performing reconstruction on projection data obtained in a scan (for example, see Patent Document 1). The method displays the reconstructed image on a display device or the like in the order of the image production, for example. If the speed of reconstruction is slow relative to that of scanning, the position being scanned does not coincide with the position of the image being reconstructed and displayed.
There is a method of performing reconstruction at a scan position selected by a user at a higher priority. In the case of such a method, the X-ray CT apparatus interrupts current reconstruction processing upon the selection of a certain position by a user during a scan by the scan gantry, and uses the latest projection data at the time of the selection to perform reconstruction. However, since the X-ray CT apparatus interrupts reconstruction processing to perform reconstruction at the certain position only after the user has selected a scan position, there is a lag between the selection of the position by the user and the display of a desired image by the X-ray CT apparatus.
Moreover, to select a certain position in this method, the user confirms a display indicating a scan time or a scan position, and visually identifies a position in the subject. It is difficult, however, for the method to provide accurate position information. Consequently, even if the user selects a scan position with such a method, a reconstructed image may be offset from the expected position.
[Patent Document 1] Japanese Patent Application Laid Open No. 2001-190538.